Saving Tomato Seeds? Ferment!

How to soak tomato seed in its own gel for best germination.

Fermentation, the biological process that converts sugars to gas, acids or alcohol accomplished by bacteria or yeast is the process that produces yogurt, sauerkraut and pickles as well as wine and beer. In a sense, it’s a tool, one that we humans use to our advantage. One of its many beneficial applications comes when saving tomato seeds for next season’s planting.

Tomato seeds, like peas and beans, are among the easiest seeds to prepare and save. But they’re not without problems. I remember my first tomato seed saving attempts. We strained the seeds out of tomato pulp, washed them, and let them dry without heat in our food dehydrator. The following spring, we planted as many starter pots as we thought we’d need tomatoes. While we did get a few seeds to germinate, the vast majority did not. Our circle of garden advisers thought maybe we’d saved the wrong seeds, namely hybrids, that have all sorts of problems when carried over a season. We hadn’t. Most thought that drying them in our dehydrator had done them in, even though we did it with the heating element turned off. That didn’t seem likely.

But the wisest among our garden consults said that we simply needed to ferment our seeds. We had no idea of what he was talking about, so when the time came he took us over to his house to show us how to do it. But not without first telling us why.

Basically, seed fermentation is just the process of letting seeds soak in their own juices or “gel” until the juices start to show mold. This is a sign that fermentation is going on. What the fermentation does is turn the tomato’s sugars to alcohol that then destroy a germination inhibitor that’s natural to the seed. Why has the plant evolved with reproductive seeds that have a component that inhibits the process? To prevent them from germinating too soon. Think of a tomato left to its own devices in nature. The fruit matures and falls to the ground. Without the inhibitor — and with everything it needs to sprout — the tomato seeds will start to germinate in their own juices even before winter has set in. The inhibitor sees to it that they don’t.

The fermentation process has other benefits. The alcohol and other products produced by fermentation will kill off any seed-borne illnesses that your tomato seeds may carry. And its also a chance to go carefully through your seeds and pick out any that are just no good. How do you do it?

First, consider all the rules of seed saving before you start. The most important is to know your tomato. You may love the tomatoes those hybrid seeds produced but saving their seed is an exercise in frustration. I’m sure we don’t need to tell you wise growers why. But even wise growers can mix up tomatoes after their picked so be sure to track the ones, usually heirlooms, that you want to save seed from. Other than that, the rules for saving tomato seed prior and after fermentation are pretty much the same.

Fermenting the seeds is easy. Choose the best looking tomatoes for their superior genetic traits. One tomato of each kind will do most gardeners unless you’re growing rows of tomatoes or want to give seeds to neighbors and friends. Slice them in half horizontally and scoop out the seeds with their accompanying gel into a glass jar. Cover the top of the jar with cheesecloth — you want your little fermenters to breathe — and leave it in a not-too-cool, dark place for a day or two. Check it regularly. Too much time will encourage your little seeds to rot or even sprout. Here’s a good guide — with pictures! — to show you the way.

What you’re doing is creating the same conditions the tomato would have if left to its own devices. When the fruit falls to the ground, it slowly rots — ferments — with the seeds inside. Weather, in the form of rains, drying sunlight and winter, will eventually decay the fruit to nothing, leaving behind only the seeds. But during the tomatoes first days on the ground after ripening, the fermentation process occurs naturally.

Once that mold starts to form in two or three days, scoop it off with a spoon and then separate the seeds from the gel. Let them dry on newspaper somewhere where its warm (but not too warm) and dark. Air circulation is good. Be sure to keep your seed labeled all through the process. When they’re fully dry, store them in a cool dark place inside a tightly closed jar. Then, at the tail end of winter, eight weeks before the last frost. . . well, you know what to do.

2 Responses to “Saving Tomato Seeds? Ferment!”

Thanks Eric – I read how to do this from an Organic Gardening enewsletter last year and saved seeds from our favorite heirloom which we don’t know what it is because Baker Creek sent us the wrong seeds. They are incredible, and this is our third year growing them. They are up to 5″ in diameter, incredibly juicy and tasty. We sold over 100 plants at the Farmers Market in Helena this spring so are spreading the joy around our valley. And we got over 90% germination rate which just shows this is the proper way to save seeds!

Be warned that saving seeds of hybrid tomatoes is westing your time, as hybrid tomato seeds will likely not produce tomatoes that are true to their type. By definition, a hybrid tomato plant is a cross between two different varieties. A hybrid variety can be re-created only by crossing the exact same two types of parent plants.